A single phase motor will need the capacitor, this is what will keep your charge to get the motor spinning full speed.
To find your torque
HP (guess 1/4 hp) x 5250
____________________
rpm
your rpm on a fan full speed should be around 1800-2000 rpm (lots of variables here)
That will give you around .72 lb/ft torque
to find your true rpm
120 x frequency
____________
number of poles
The scrapyard is the best source for electric motors there is. People scrap out good motors all the time. Do your diligence and get a list of what you want from the motor. can usually buy them at 1/100 of the price as a new one. just make sure they spin and you don't hear/feel any rubbing or scraping. there shouldn't be an issue with bearings as you have the belt setup / arbor for the grinder you just need more torque from your motor 1 hp should be more than enough.
last motor i bought from the yard was wired with a plug and toggle switch... good to go no messing around wiring or guessing and cost me 7 bucks.
belt tension is gonna have to be tight or it will start to slip as soon as you apply to much pressure to the wheel.
Good luck
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